'Crash diets' studied for type 2 diabetes

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Behind the Headlines

Friday June 24 2011

Many people with diabetes monitor blood glucose at home

“A crash diet could end the misery of type 2 diabetes for millions of sufferers,” reported the Daily Mirror. It said a study has found that a “special 600-calories-a-day eating plan cuts fat in the pancreas and prompts insulin cells to wake up after just eight weeks”.

Many newspapers covered this study, and most claimed that it has found a “cure”. However, this was a very small, preliminary study in only 11 obese people with type 2 diabetes. Referring to this diet as a cure exaggerates the significance of the findings.

The study tested the theory that severely restricting the amount of energy in the diet can reverse the body’s resistance to insulin, which occurs in type 2 diabetes, and halt the progressive decline in function of pancreas cells that produce insulin.

Very limited conclusions can be drawn from the study’s findings, and much further research is required. Alone, this study provides no evidence of a cure for diabetes. People with type 2 diabetes should continue to follow the dietary advice given to them by their doctor. The participants in this study were all given medical supervision throughout, and people with the condition are advised not to try this diet on their own.

Where did the story come from?

The study was carried out by researchers from the Human Nutrition Research Centre at Newcastle University. Fundjng was provided by Diabetes UK. The study was published in the peer-reviewed medical journal Diabetologia.

Many of the news stories have exaggerated the implications from the findings of this very small, preliminary study.

What kind of research was this?

This research investigated whether an energy-restricted diet had an effect on the biochemical signs of type 2 diabetes in people with the condition. Type 2 diabetes occurs when not enough insulin is produced by the pancreas for the body to function properly, or when the body’s cells do not react to insulin. Insulin is a hormone that helps the body use glucose for energy. The condition is progressive as the increased demand on the pancreas to create more insulin leads to further decline in function of the insulin-producing beta cells. Many people who have type 2 diabetes for a long time have to start injecting insulin as their condition worsens.

The researchers wanted to see whether their diet could reverse the resistance of the body’s cells to the actions of insulin, and prevent progressive decline in function of beta cells.

This research was a non-randomised, study in 11 people with type 2 diabetes. For comparison, the researchers also conducted one-off measurements in nine people without diabetes who did not receive the dietary intervention. However, this was not a controlled study as there was no comparison group of people with diabetes who received a comparison intervention (such as an alternative diet) or no dietary intervention.

The researchers say that previous studies have found that weight-loss surgery can help reverse diabetes. This gave them the idea that a sudden negative energy balance, taking in fewer calories than the body burns, could have a profound effect on metabolism (the rate at which the body turns food into energy). Excess concentrations of fatty acids are also said to inhibit the function of beta cells, so it was expected that a decrease in fatty acid levels would improve the function of these cells.

What did the research involve?

The researchers recruited 15 people with type 2 diabetes. Their average age was 49.5 and they had an average body mass index (BMI) of 33.6 (which is classed as obese). The participants had had type 2 diabetes for less than four years. In the weeks leading up to the study, their diabetic medications (metformin in seven people and sulfonylurea in two) were withdrawn. Eleven people with diabetes and eight without the condition completed the study, and the researchers reported the findings for these people only.

Laboratory methods were used to assess insulin sensitivity of the liver and other body tissues at the start of the study, in addition to the level of glucose output from the liver. A special type of MRI scan was used to measure the fatty acid (triacylglycerol) content of the liver and pancreas. The people then began a diet of nutrient drinks (46.4% carbohydrate, 32.5% protein and 20.1% fat, plus vitamins, minerals and trace elements), which supplied 510 calories a day (kcal/day). This was supplemented by three portions of non-starchy vegetables to give a total energy intake of 600 kcal/day. Further measurements were taken at one, four and eight weeks after starting the diet. At eight weeks, the participants returned to normal eating, but MRI scans were carried out again at 12 weeks.

The comparison group of nine people without diabetes were matched to the people with diabetes in terms of their age, sex and weight. One-off measurements were taken from these people at the beginning of the study. These people received no dietary intervention.

What were the basic results?

After one week of the restricted-energy diet, fasting plasma glucose (blood sugar levels) normalised (decreasing from an average of 9.2 to 5.9 millimoles per litre). The production of glucose from the liver also decreased, and the liver’s sensitivity to insulin improved from 43% at the beginning of the study to 74% after one week. By week eight, the fatty acid content of the liver had fallen from 12.8% at the study’s start to 2.9%, while levels in the pancreas fell from 8.0% to 6.2%. The sensitivity of pancreatic cells to glucose improved over the eight weeks of the intervention.

The researchers did not notice a change in the insulin sensitivity of other body tissues apart from the liver.

Over the eight weeks of the diet, the average weight loss was 15.3kg (equivalent to 15% of the participants’ initial bodyweight). By 12 weeks (four weeks after the diet was stopped), participants had gained an average 3.1kg in weight. Decreases in triacylglycerol content of the liver and pancreas were maintained after the participants came off the diet, but fasting blood sugar increased.

How did the researchers interpret the results?

The researchers concluded that a restricted-energy diet brought the function of pancreatic beta cells back to normal and improved the sensitivity of the liver to insulin in people with type 2 diabetes. The amount of fat stored in the pancreas and liver also decreased.

Conclusion

This was a very small preliminary, non-randomised, uncontrolled study. Only 11 people with diabetes received the dietary intervention. Although the researchers took one-off measures in eight people without diabetes for comparison, these people did not follow the diet. There was also no comparison group of people with diabetes who did not receive the diet intervention.

As such, very limited conclusions can be made from this study. Contrary to some news reports, it provides no evidence of a cure for diabetes.

Importantly, the study only examined the effects of eight weeks of an extreme energy-restriction diet, where the daily intake was only 600 calories. The longer-term health implications and risks of such a diet are not known.

Carefully conducted randomised controlled dietary studies in a much larger number of people with type 2 diabetes, and with longer follow-up, are needed. This research will need to carry out a more detailed assessment of the possible effects of such an intervention on diabetic control and on health in general. It will also need to ascertain whether the positive effects seen in this study are sustained when a person returns to a normal diet.

People with type 2 diabetes should continue to follow the dietary advice given to them by their doctor. The participants in this study were all given medical supervision throughout, and it is advised that people with the condition do not attempt this diet on their own.

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